我正在尝试编写一个简单的SprintBoot REST控制器,以便在Websphere Liberty上运行,并且遇到@Autowire的问题。以下是相关的(我认为)代码片段:
@CrossOrigin
@RestController
@RequestMapping(path = "userSetting")
public class RESTInterface {
@Autowired
private UserSettingDAO userSettingDAO;
@RequestMapping(path = "/getUserSetting", method = { RequestMethod.GET }, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
public String getUserSetting(
@RequestParam(value="user_id", required=true ) String user_id,
@RequestParam(value="app_id", required=true ) String app_id,
@RequestParam(value="dashboard_name", required=true ) String dashboard_name
) {
if ( userSettingDAO == null ) {
System.out.println( "userSettingDAO is null" );
...
////////////////////////////////////////////////////////////////////////////////
@Component
public class UserSettingDAO {
@Autowired
private JdbcTemplate jdbcTemplate;
@Autowired
private DataSource dataSource;
public UserSettingDAO() {
System.out.println( "dataSource is " + dataSource );
System.out.println( "jdbcTemplate is " + jdbcTemplate );
当我将应用程序部署到Liberty时,它似乎启动正常。
当我点击相应的端点时,我会在console.log
中看到以下内容:
UserSettingDAO.jdbcTemplate = null
dataSource is null
jdbcTemplate is null
2018-04-24 16:54:19.887 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/userSetting/getUserSetting],methods=[GET],produces=[application/json;charset=UTF-8]}" onto public java.lang.String com.ui.usersetting.restinterface.RESTInterface.getUserSetting(java.lang.String,java.lang.String,java.lang.String)
2018-04-24 16:54:19.890 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/userSetting/upsertUserSetting],methods=[POST],produces=[application/json;charset=UTF-8]}" onto public void com.ui.usersetting.restinterface.RESTInterface.upsertUserSetting(java.lang.String,java.lang.String,java.lang.String,java.lang.String)
2018-04-24 16:54:19.891 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/userSetting/deleteUserSetting],methods=[DELETE],produces=[application/json;charset=UTF-8]}" onto public void com.ui.usersetting.restinterface.RESTInterface.deleteUserSetting(java.lang.String,java.lang.String,java.lang.String)
2018-04-24 16:54:19.893 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/userSetting/hello],methods=[GET],produces=[application/json;charset=UTF-8]}" onto public java.lang.String com.ui.usersetting.restinterface.RESTInterface.hello()
2018-04-24 16:54:19.924 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2018-04-24 16:54:19.925 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-04-24 16:54:20.166 INFO 8807 --- [cutor-thread-11] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6a5997f7: startup date [Tue Apr 24 16:54:15 EDT 2018]; root of context hierarchy
2018-04-24 16:54:21.386 INFO 8807 --- [cutor-thread-11] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2018-04-24 16:54:21.389 INFO 8807 --- [cutor-thread-11] o.s.j.e.a.AnnotationMBeanExporter : Bean with name 'dataSource' has been autodetected for JMX exposure
2018-04-24 16:54:21.396 INFO 8807 --- [cutor-thread-11] o.s.j.e.a.AnnotationMBeanExporter : Located MBean 'dataSource': registering with JMX server as MBean [com.zaxxer.hikari:name=dataSource,type=HikariDataSource]
我的问题是:为什么两个println
语句说他们各自的变量是空的?它是否与UserSettingDAO构造函数出现在要执行的日志之前中有关dataSource
的行出现在日志中这一事实有什么关系?
答案 0 :(得分:0)
在调用Spring组件的构造函数时,任何@Autowired
对象仍将为null。这是因为spring容器需要初始化类的实例才能将值注入@Autowired
字段。
我不知道Spring如何实现注入,但大多数Java注入都是这样的:
为验证这一点,我在UserSettingsDAO
上创建了一个利用@AutoWired
字段的方法:
@Component
public class UserSettingDAO {
@Autowired
private JdbcTemplate jdbcTemplate;
@Autowired
private DataSource ds;
public UserSettingDAO() {
System.out.println("ctor/jdbcTemplate is " + jdbcTemplate );
System.out.println("ctor/datasource is: " + ds);
}
public void doStuff() {
System.out.println("doStuff/jdbcTemplate is " + jdbcTemplate );
System.out.println("doStuff/datasource is: " + ds);
}
}
如果我们将这个DAO注入另一个类并使用它,我们将看到在构造UserSettingDAO
之后字段被初始化:
@CrossOrigin
@RestController
public class RESTInterface {
@Autowired
private UserSettingDAO dao;
@RequestMapping(path = "/jdbc", method = { RequestMethod.GET }, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
public String jdbc() {
return dao.doStuff();
}
}
检查日志,这将产生以下输出:
ctor/jdbcTemplate is null
ctor/datasource is: null
doStuff/jdbcTemplate is org.springframework.jdbc.core.JdbcTemplate@4eb46bed
doStuff/datasource is: com.ibm.ws.rsadapter.jdbc.WSJdbcDataSource@727d23c5